This invention is directed to the art of glass manufacturing and more specifically is directed to an improvement in the area of handling hot glass charges or gobs as well as newly-formed glass articles. The invention provides a method of preparing heat-resistant lubricious surfaces which are able to convey or handle such glass charges or articles without deleteriously affecting the contacting surfaces of the charges or articles.
In one common method of glass manufacture, charges or gobs of molten glass are severed from a supply body or feeder for molten glass and are conveyed by free fall over chutes to molds or other apparatus for forming the glass articles.
Important considerations are involved in conveying the gob or charge from the glass feeder to the mold or other forming mechanism. Initially, the time interval of travel must be constant in order to ensure efficient and uniform operation. Secondly, the gob shape must not be seriously altered during travel since any marked alteration may cause distortion or irregularities in the finished article. Thirdly, the surface of the gob must not be unduly chilled or contaminated in the manufacture of high-quality glassware.
Where the chutes for conveying the glass are plain metal or other untreated material, the hot glass gob exhibits a tendency to become adhered thereto resulting in either a failure to travel to the mold in the required time or a distortion of the gob shape. The gob is caused to slow down or is dragged by excessive or uneven temperature conditions of the chute. To overcome such problems, it has been common practice to lubricate the chute by either an intermittent or continuous flow of oil or an oil-based dope. Such treatment of the chute facilitates the passage of the glass but is only a temporary treatment and necessitates frequent or continuous application of the oil or oil-based dope. Despite such continued application, the travel time of the glass gob is frequently extremely erratic and not constant. Also, the oil dope has a tendency to form carbonaceous deposits on the gob which are carried into the finished article. The extreme variation in lubrication may also cause the gob to become scratched or marred producing scars or imperfections in the finished article. In addition, the oil and water which are usually present in the area of glass forming apparatus if excessive tend to further complicate the problem of lubrication by forming deposits on the chute working surface which adversely affect the lubricating action.
It is known that satisfactory coatings for chutes must meet the following requirements: First, the frictional drag must be reduced to a minimum so that downward travel of the gob by gravity is fast and constant, and the shape of the gob is not altered. Second, the coating must be hard and abrasion resistant in order not to contaminate the surface of the gob and to resist rapid wear of the chute surface. Third, the coating must be extremely resistant to heat. Fourth, the coating must be resistant to oil and water which are frequently present in the vicinity of the apparatus.
In the prior art, such coatings have frequently been of the type which include a thermosetting resin and a lubricating filler such as graphite or molybdenum disulphide. Such coatings are disclosed in U.S. Pat. No. 2,758,421 to R. M. Smith, issued Aug. 4, 1956, entitled, "Chute For Conveying Molten Glass", which patent is assigned to the same common assignee as the present application.